This invention relates generally to regulating AC bus voltage in power distribution grids and more particularly to regulating AC bus voltage in power distribution grids having distributed power generation resources.
An increasing number of distributed power generation resources (such as solar panels, wind turbines, fuel cells, microturbines and the like) are being connected to low or medium voltage AC buses within the utility power distribution grid. Many distributed power generation resources are coupled to the grid through electronic power converters that have the inherent capability of rapidly synthesizing reactive power load (leading or lagging) for the grid, in addition to any real power being supplied from the power source.
The real power available from renewable power sources such as solar or wind tends to be variable, so that the KVA rating of distributed power converters is often only partially utilized in delivering real power to the grid. If the real power output of a distributed power converter is curtailed so that less than its rated KVA capability is used for real power transfer, the unused capability may be deployed for the useful generation of reactive power.
It is possible, but impractical, for a centralized grid control center to make decisions about the level of reactive power needed at a particular bus at any time in order to raise or lower the prevailing bus voltage. For example, an operator or a computer at the control center would notice high or low voltage at an inverter bus and dispatch a request for the inverter to change its reactive power output. This extremely slow time frame renders such reactive control methods impractical.
Another problem with renewable distributed power generation resources is that the fluctuations of the real power output from these sources cause variations in the distribution bus voltages (mainly due to the resistance of the distribution power circuits). This problem tends to limit the fraction (or “penetration”) of renewable distributed power generation resources relative to conventional load that can be connected to a power distribution grid.